fix(client): skip output schema validation on error results

[codefromthecrypt]

Motivation and Context

The MCP Inspector client failed tool calls that returned isError: true alongside structuredContent, because the SDK still validated the output schema even on error results.

How Has This Been Tested?

new tests and manual

Breaking Changes

None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Before:

$ node ~/oss/inspector/cli/build/cli.js \
    http://localhost:64345/stream \
    --cli --transport http \
    --method tools/call \
    --tool-name get_repositories
Failed to call tool get_repositories: MCP error -32602: Structured content does not match the tool's output schema: data must have required property 'roots'

Failed with exit code: 1

After:

$ node ~/oss/inspector/cli/build/cli.js     http://localhost:64345/stream     --cli --transport http     --method tools/call     --tool-name get_repositories
{
  "content": [
    {
      "type": "text",
      "text": "No exact project is specified while multiple projects are opened.\n You may specify the project path via `projectPath` parameter when calling a tool. \n If you're aware of the current working directory you may pass it as `projectPath`. \n In the case when it's unobvious which project to use you have to ASK the USER about a project providing him a numbered list of the projects.\n Currently open projects: {\"projects\":[{\"path\":\"/Users/codefromthecrypt/oss/observability-examples/genai-function-calling/spring-ai\"},{\"path\":\"/Users/codefromthecrypt/oss/koog\"},{\"path\":\"/Users/codefromthecrypt/oss/intellij-community/plugins/mcp-server\"}]}"
    }
  ],
  "structuredContent": {
    "projects": [
      {
        "path": "/Users/codefromthecrypt/oss/observability-examples/genai-function-calling/spring-ai"
      },
      {
        "path": "/Users/codefromthecrypt/oss/koog"
      },
      {
        "path": "/Users/codefromthecrypt/oss/intellij-community/plugins/mcp-server"
      }
    ]
  },
  "isError": true
}

[changeset-bot]

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Latest commit: a9ff608

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[pkg-pr-new]

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npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/sdk@1428

commit: a9ff608